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Thread: Another new pool owner; dark spots around drain w/high CH

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    Join Date
    May 2015
    Location
    Riverview, FL
    Posts
    2

    Question Another new pool owner; dark spots around drain w/high CH

    Hello!

    We have moved into a home with an inground marcite finish pool. It is 11000 gallons. We know very little about it and have never owned a pool before, but when we decided on this house we found TTFP and have been reading up.

    About a week after moving in, about a dozen dark brown spots, varying in size from dime to nickel sized, began appearing around the drain at the deep end of the pool. Reading here, the suggestion was to lower the pH to 6.8 with muriatic acid and scrub the bejeezus out of them, and then raise the pH when we get the stains out. We've been doing this the past 2-3 days without much improvement. The calcium hardness is quite high, and when I run that particular test, I am getting purple before I get blue, which makes me think there is metal in the water.

    The water itself is relatively clean and clear. I do feel like the marcite surface is dingy, and don't really know how to remedy that. Also, the drain cover has been stained since we moved in.

    Today's tests with our Taylor K-2006 kit:

    FC: 3.6
    pH: 6.8
    TA: 75
    CH: 500
    CYA: 70

    These are all in line with the pool manufacturer's recommendations, except for the CH, and the TA is maybe a touch low, but had been fine until today at 80-100.

    DSCN0311.jpgDSCN0320.jpg

    These photos were taken at night, so they don't necessarily accurately depict the color of the water.

    Any suggestions?

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    Richard320's Avatar
    Join Date
    Jan 2010
    Location
    San Dimas, CA (LA County)
    Posts
    18,768

    Re: Another new pool owner; dark spots around drain w/high CH

    Welcome!

    Those look like rust.

    I will tell you from sad experience that the tiniest piece of steel - I'm talking the size of a grain of salt - can leave a quarter inch rust spot. Don't use a hacksaw to cut metal anywhere near the pool. Setting a vitamin C tablet on it will probably lift it. Just a cheap generic Vitamin C tablet. If you don't want to swim down to it, put a few in a nylon with a clean smooth rock and set that opn to. push it into position with the pool brush.
    There's more in Pool School - Metals in the Water and Metal Stains


    As for the CH test, With your levels, use the 10 ml sample mentioned in Extended Test Kit Directions and also read the note about adding some R-0012 before you add the R-0010.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  3. Back To Top    #3

    Join Date
    May 2015
    Location
    Riverview, FL
    Posts
    2

    Re: Another new pool owner; dark spots around drain w/high CH

    Excellent, thanks!

    I have been using the 10ml sample after the very first time I tested...otherwise that's a LOT of drops!

    I will get some Vit C tomorrow and try it out. I hope it works, although I really don't know where it could be coming from. The pool is screened in.
    10771 gallon inground marcite pool Taylor K2006 kit 127 BTU Sunrunner Heat Pump

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